What Are
the Most Common Forms of Genetic Hearing Loss?
Of the 50% of the genetic forms of hearing loss, an estimated
70% are due to recessive causes, about 15% have a dominant
cause; and the remaining 15% include all the other forms
of inheritance.

GENETIC

RECESSIVE
70%

NON-GENETIC
AND UNKNOWN

DOMINANT
15%

OTHER
GENETIC 15%

Genetic scientists subdivide
genetic hearing loss into two general categories: "Non-Syndromic"
(meaning hearing loss and nothing else) and "Syndromic"
(meaning hearing loss with other clinical findings). By
far, the more common is Non-syndromic hearing loss which
includes 2/3 of all genetic hearing losses.

SYNDROMIC

NON-SYNDROMIC

RECESSIVE

RECESSIVE

NON-GENETIC
AND UNKNOWN

DOMINANT

DOMINANT

OTHER
GENETIC

OTHER
GENETIC

What is the Most Common form
of genetic hearing loss?
One gene, known as Connexin 26 (abbreviated CX26), is estimated
to be responsible for half of all the recessive cases of
hearing loss. There are over 400 known genetic causes involving
hearing loss. CX26 alone is responsible for about 1/3 of
all the cases of genetic hearing loss!

SYNDROMIC

NON-SYNDROMIC

RECESSIVE

CONNEXIN-26

NON-GENETIC
AND UNKNOWN

RECESSIVE

DOMINANT

DOMINANT

OTHER
GENETIC

OTHER
GENETIC

What are the Next Most Common
Forms of Genetic Hearing Loss?
Since CX26 accounts for about 1/3 of all cases of genetic
hearing loss, that leaves about 1/3 of all cases as non-syndromic
(this includes all types of inheritance) with the remaining
1/3 as syndromic. Among the remaining 1/3 of non-syndromic
cases of genetic hearing loss, 13 dominant and 8 other recessive
genes have been described.

What are the Common Dominant Syndromic
Hearing Loss Types?
The following descriptions are only a brief review. Medical
professionals can guide you for further information. About
5% of all hearing loss is dominant syndromic in nature.
http://www.familyvillage.wisc.edu/index.htmlx

Branchio-Oto-Renal (BOR) Syndrome
- The hearing loss in BOR Syndrome is conductive, sensorineural or mixed. Cysts (or pits) can be found on the neck (branchial cleft) or in front of the outer ear (prearicular). The outer ear (pinna) may be malformed and stapes fixation, inner ear malformations and/or enlarged vestibular aqueducts may be present. A major medical concern with BOR are the associated renal (kidney) problems, which could be life threatening. http://www.boystownhospital.org/Hearing/info/genetics/syndromes/bor.asp

Stickler
Syndrome - The hearing loss in Stickler Syndrome is
usually conductive, although some losses may be mixed
or sensorineural. Progressive hearing loss has also been
reported. There are three syndrome types. All are related
to altered expression of a collagen/connective tissue
gene. Associated features may include: cleft palate, downward-placed
tongue (glossoptosis), small jaw (micrognathia), under-developed
midface, progressive severe near-sightedness (myopia),
cataracts, retinal detachment/degeneration, bone/joint
disorders, early adult-onset arthritis, and middle ear
bone (ossicular) malformations. http://www.sticklers.org/sip/

What are the Common Recessive Syndromic
Hearing Loss Types?
Recessive Syndromic hearing loss accounts for about 20%
of all types of genetic hearing loss.

Usher Syndrome - There are three (3) types of Usher syndrome with different types of hearing loss. Type I has congenital, profound, sensorineural hearing loss. And vestibular dysfunction. Type II has a downward-sloping, sensorineural hearing loss. Type III has a progressive sensorineural hearing loss and variable vestibular dysfunction. All types have progressive vision loss. http://www.nidcd.nih.gov/health/hearing/usher.asp

Alport Syndrome - Hearing
loss in Alport syndrome may be sensorineural, conductive
or mixed and may be progressive. Alport syndrome may also
be X-linked (linked to sex-chromosome inheritance). Other
features include kidney problems (nephritis), near-sightedness
(myopia) or cataracts, and palate abnormalities. http://www.cc.utah.edu/~cla6202/ASHP.htm

Jervell
and Lange-Nielson Syndrome - The hearing loss in JL-N
syndrome is sensorineural. The other major finding in
JL-N is an abnormal heart rhythm (long Q-T), which could
lead to fainting spells and possible sudden death. These
might be mistaken for seizures. These abnormal heart rhythms
are successfully treated with medication (beta blockers).

CHARGE Syndrome
- The letters in CHARGE stand for Coloboma, Heart, Atresia
of the choanae, Retardation of growth and development,
Genital and urinary abnormalities, and Ear abnormalities.
CHARGE is thought to be multifactorial. The hearing loss
may be conductive, sensorineural or mixed and range from
mild to profound. In addition to the features in the name,
there may be partial facial paralysis, cleft palate, cleft
lip, kidney problems, and feeding problems due to an opening
between the windpipe and the feeding tube. http://www.chargesyndrome.org/

X-Linked Congenital Stapes Fixation
with Perilymph Gusher - For boys with this syndrome,
the hearing loss is mixed and may be progressive. Females
who carry this gene may have mild, mixed or sensorineural
hearing loss. Boys with this gene have a further risk
of increased hearing loss if middle ear surgery is performed
to correct the stapes fixation because the surgery may
result in massive and sudden loss of inner ear fluid (perilymph).

Mitochondrial ConditionsMitochondria
are structures in the cell that produce the energy that
cells need to survive. Neither the mitochondria nor the
cell can exist without the other. Interestingly, mitochondria
have a separate set of genes that are not part of the
cell's genes. This is because mitochondria originally
came from energy-producing bacteria that merged with the
cell. Anything that affects bacteria could also affect
the function of the cell's mitochondria, which might eventually
affect the cell's energy source. Changes in the mitochondrial
genes can also result in syndromes involving hearing loss.

1555DELG
- The hearing loss is sensorineural and may be progressive.
Those who have this condition may have sudden hearing
loss when exposed to aminoglycoside antibiotics (e.g.,
neomycin, gentamycin, streptomycin, kanamycin, tobramycin,
or amikacin).